1. Field of the Invention
The present invention relates to an image reading apparatus. It also relates to a light guide member used for an image reading apparatus.
2. Description of the Related Art
As is well known, a typical image reading apparatus incorporating a linear image sensor is designed to illuminate an image read line of a document with light emitted from a light source. The light reflected at the image read line is received by a plurality of light receiving elements. Each of the light receiving elements outputs signals corresponding to the received amount of light.
With such an image reading apparatus, if the image read line is not illuminated sufficiently, the image reading quality may be deteriorated. Therefore, light emitted from the light source needs to be effectively directed to the image read line. For this purpose, JP-A-9-307696 for example discloses an image reading apparatus in which a light guide member (prism) is arranged in facing relationship to a light source for guiding light emitted from the light source toward an image read line. In this image reading apparatus, light from the light source can be directed toward the image read line even if the light source is not disposed in facing relationship to the image read line.
In the above-described image reading apparatus, the light guide member has a flat light incidence surface. Light entering the light guide member through the light incidence surface is emitted through a light exit surface toward the image read line. However, the light guide member with the flat light incidence surface has the following problems.
Generally, light emitted from the light source has a tendency to diverge as it travels. Since the light incidence surface of the prior art light guide member is flat, the light entering the light guide member through the light incidence surface continues to diverge within the light guide member. Therefore, the amount of light directed toward the light exit surface is reduced. Specifically, most of the light entering the light guide member travels toward the light exit surface while being totally reflected by the surfaces of the light guide member. However, since light disperses in various directions within the light guide member, a large amount of light impinges on the surfaces of the light guide member at an angle smaller than the total reflection critical angle, thereby passing through the light guide member. As a result, the amount of light guided toward the light exit surface is reduced, resulting in deterioration of the image reading quality.
Moreover, even if a large amount of light is guided toward the light exit surface, it is difficult to efficiently illuminate the image read line because the light is not converged.
Thus, the prior art image reading apparatus needs to be improved to enhance efficiency in illuminating the image read line.
It is therefore an object of the present invention to provide an image reading apparatus which is capable of effectively illuminating an image read line of a document.
An object of the present invention to provide a light guide member which may be advantageously incorporated in such an image reading apparatus.
In accordance with a first aspect of the present invention, an image reading apparatus comprises at least one light source, an elongate light guide member for guiding light emitted from the light source toward an image read line, and a plurality of light receiving elements for receiving light reflected at the image read line. The light guide member includes a first portion, a second portion, and a connecting portion for connecting the first portion and the second portion. The first portion includes a light incidence surface facing the light source for entry of light emitted from the light source, and the light incidence surface is convexly curved widthwise of the light guide member. The second portion includes a light exit surface oriented toward the image read line for emitting light toward the image read line. The connecting portion is narrower than the first portion and the second portion.
Preferably, the first portion of the light guide member further may include additional light exit surfaces each of which is convexly curved, whereas the second portion of the light guide member may further include an additional light incidence surface facing each light exit surface of the first portion.
Preferably, the first portion, the second portion and the connecting portion may be formed of transparent resin as one piece.
Preferably, the connecting portion may be located on a widthwise center axis of the first portion, and the widthwise center axis of the first portion may be located directly above the light source.
Preferably, the light exit surface of the second portion may be convexly curved at least partially.
Preferably, the light exit surface of the second portion may be offset widthwise toward the image read line relative to the light incidence surface of the first portion.
According to a second aspect of the present invention, there is provided an image reading apparatus which comprises at least one light source, an elongate light guide member for guiding light emitted from the light source toward an image read line, and a plurality of light receiving elements for receiving light reflected at the image read line. The light guide member includes a first portion, a second portion, and a connecting portion for connecting the first portion and the second portion. The first portion includes a first light incidence surface facing the light source for entry of light emitted from the light source, and at least one first light exit surface facing the second portion and convexly curved. The second portion includes at least one second light incidence surface facing the first light exit surface of the first portion for reentry of light, and a second light exit surface oriented toward the image read line for emitting light toward the image read line. The connecting portion is narrower than the first portion and the second portion.
According to a third aspect of the present invention, there is provided an elongate light guide member which comprises a first portion, a second portion, and a connecting portion connecting the first portion and the second portion. The first portion includes a light incidence surface oriented away from the second portion for entry of light and convexly curved widthwise of the light guide member. The second portion includes a light exit surface oriented away from the first portion for emitting light. The connecting portion is narrower than the first portion and the second portion.
Preferably, the first portion of the light guide member may further include additional light exit surfaces each of which is convexly curved, and the second portion of the light guide member may further include an additional light incidence surface facing each light exit surface of the first portion.
Preferably, the first portion, the second portion and the connecting portion may be formed of transparent resin as one piece.
Preferably, the connecting portion may be located on a widthwise center axis of the first portion.
Preferably, the light exit surface of the second portion may be convexly curved at least partially.
Preferably, the second portion includes a pair of side surfaces which are inclined with respect to a widthwise center axis of the first portion.
According to a fourth aspect of the present invention, there is provided an elongate light guide member which comprises a first portion, a second portion, and a connecting portion connecting the first portion and the second portion. The first portion includes a first light incidence surface oriented away from the second portion for entry of light, and at least one first light exit surface facing the second portion and convexly curved. The second portion includes at least one second light incidence surface facing the first light exit surface of the first portion for reentry of light, and a second light exit surface oriented away from the first portion for emitting light. The connecting portion is narrower than the first portion and the second portion.
Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings.